Radio frequency direction finding antenna systems are useful in a number of applications which require accurate determination of the direction from which a radio transmission originates. Communication systems that depend on mobile transmitters or receivers, or satellites, use direction finding to determine proper orientation of a receiving antenna. Surveillance, intelligence, and military targeting systems are primarily concerned with accurate location of a radio frequency source.
The most prevalent radio direction finding systems include a paraboloid off-set antenna which comprises a reflector having the shape of a parabolic section, a feed horn fixed at the focal point of the reflector, a motor for rotating the reflector and feed horn together as a unit (and position indicators for communicating the exact orientation of the reflector and feed horn), and associated electronics for controlling the motor, processing received signals, and generating an output indicating the direction of a radio frequency signal of interest. While the reflector and feed horn are rotated together, associated signal processing systems analyze detected RF signals to determine the direction from which RF signals of interest originate. The direction of a received signal is determined by comparing the position information of the antenna and feed horn with the peak beam strength of the incoming signal.
Non-rotating direction finding antenna systems have been proposed, and these operate as phased arrays. These systems comprise a number of antennae located in fixed relationship to each other, and associated electronics for processing received signals, and generating an output indicating the direction of a radio frequency signal of interest. These systems entail relatively large arrays, and are generally planar, and provide coverage over limited spans.